Before the shutter opens

Plan star trails on your own frame

Place the celestial pole, enter the timing of the sequence, and see how long the trails and the gaps will be at different places in the picture. The optional photograph never leaves this tab.

The shoot

Sequence

Session minutes Exposure seconds Start-to-start interval seconds Average frame MB Card capacity GB Storage headroom %

Camera and frame

Orientation Focal length mm Sensor width mm Sensor height mm Image width px Image height px

Celestial pole

Drag on the picture, use its arrow keys, or enter a percentage. Values outside 0–100 put the pole beyond the frame.

Across frame % Down frame %

Optional photograph Choose a preview image

No photograph selected. The diagram still gives the same geometry.

Composition preview

Where the sky will draw

celestial pole measured marker

Drag anywhere to place the pole. Arrow keys move it by 1%; Shift + arrow moves it by 5%. The diamond is a fixed marker used for the pixel readout.

Sky rotation——

Sequence——

At the marker——

Across this frame—shortest to longest finished arc

Shutter closed——

Storage with headroom——

What the numbers mean

The sky rotates about the celestial pole at the sidereal rate: 15.041° per hour. A trail in this image is its radius from the pole, in pixels, multiplied by that rotation. The coloured arcs show the completed session; the marker reports one exposure’s dash and the unrecorded gap before the next frame.

This is a planning model, not a weather or visibility guarantee. A heavily distorted or fisheye lens needs the projection-aware version planned for the next release.

From plan to finished trail

Keep the real interval as close to the exposure as the camera allows, then bring the sequence back here. The stacker reads the actual timing from the frames and can compare the plan with what the night recorded.

Stack the sequence Choose a pinpoint exposure →Why gaps become dots →